It is said that soft plaque existing in a blood vessel is unstable, easily detaches from a blood vessel wall, and has a high risk to cause a blood clot. Therefore, it is desirable that the existence and distribution of soft plaque are displayed to be easily visualized.
For example, the patent literature 1 describes an image analysis device analyzing plaque associated with a blood vessel. The image analysis device displays an index showing the plaque instability according to the pixel value distribution of an image in a designated region by designating a desired region on the image.